1. Technical Field
This invention relates to the technology of extruding aluminum alloys and more particularly to such alloys that are usable in heat exchangers for automotive vehicular applications.
2. Discussion of the Prior Art
Low cost heat exchange tubes made of an aluminum alloy have been heretofore made with relatively thick walls, such as 0.60 millimeters. Such tubing has been made by a process of casting a billet and extruding or drawing the billet to produce a hollow shape, typical alloys for the billet usually contain silicon (0.3% or more by weight), iron (at least 0.4%), copper (at least 0.15%), manganese (1.0%) and the remainder aluminum.
To achieve thinner walled tubing, the extrudable characteristic of the alloy must be enhanced by employing a purer aluminum alloy containing less than about 0.3 percent by weight manganese. However, such enhanced-extrudable alloys will not meet extended life requirements because of possible corrosion and lower fatigue strength. Certain elements which retard corrosion in a nonextruded product (such as disclosed in U.S. Pat. No. 4,694,087) cannot be added to an extrusion alloy because they retard extrudability. Moreover, brazing of an extruded thin wall aluminum-based tubing often causes extensive penetration of the tubing by the elements of the brazing filler metal, thereby resulting in thinning and poor corrosion resistance from a changed microstructure.